This invention relates to a new process for applying the solid oxide electrolyte and cermet exterior electrode of high temperature solid oxide electrochemical cells, such as fuel cells.
High temperature solid oxide fuel cell configurations are well known, and taught, for example, in U.S. Pat. No. 4,490,444 (Isenberg), herein incorporated by reference. There, a porous, calcia stabilized zirconia support tube, having a 50 micrometer to 500 micrometer thick, porous air electrode of, for example calcium, strontium, magnesium or zirconium oxide doped lanthanum manganite was taught, with an attached, axially elongated, narrow interconnection strip of calcium, strontium, or magnesium oxide doped lanthanum chromite. The air electrode was coated with a 20 micrometer to 50 micrometer thick, solid, non-porous, yttria stabilized zirconia electrolyte. A porous, nickel-zirconia cermet, exterior fuel electrode, about 50 micrometers thick, covered most of the electrolyte.
The interconnection and electrolyte were applied according to the teachings of U.S. Pat. No. 4,609,562 (Isenberg et al.), and the fuel electrode was applied according to the teachings of U.S. Pat. No. 4,597,170 (Isenberg), both involving vapor deposition techniques. This processing involves three separate expensive vapor deposition steps. Elimination of any of these would significantly reduce overall cell fabrication cost.
In making flat plate electrochemical converters, U.S. Pat. No. 4,629,537 (Hsu) teaches a lengthy and complicated process including: plasma spray depositing a flat, porous, stabilized zirconia electrolyte sheet on a carbon substrate, separating the sheet from the carbon substrate, sintering the sheet at 1,400.degree. C. to 1,600.degree. C. to densify the electrolyte to 96% of theoretical density, smoothing both of the flat surfaces, and then coating each side with a nickel-zirconia fuel electrode and a strontium doped lanthanum manganite oxidizer electrode by a dip slurry or flame deposition technique, to form a cell. Corrugated plate interconnectors of nickel and platinum alloy are then placed between cells.
It is a main object of this invention to provide an inexpensive, simplified fabrication process for making high temperature, tubular, solid oxide electrochemical cells.